Almost everyone Jared Rosenthal does business with has a secret or a suspicion, something they hold close and keep confidential and do not share even with those nearest to them.
But they tell Mr. Rosenthal.
He is not a priest or a psychologist. He is not a doctor or a lawyer.
He is the owner of two trucks, each emblazoned with a slogan as blunt as it is effective, posing a simple question: “Who’s your daddy?”
The trucks — recreational vehicles that have been converted into rolling laboratories offering on-the-spot DNA testing — invariably attract stares and questions when they appear around New York City, and might seem like unlikely confessionals.
But Mr. Rosenthal, 46, said the trucks have been extraordinarily effective marketing tools, and that with DNA testing, intimate stories of intrigue and revelation are never far.
Over the years, he said, he has brought long-lost siblings together and told others that they were not, in fact, related. He has told men that the children they raised were not biologically their own. He has told others they were the fathers of children they never knew they had.
It was not exactly the career Mr. Rosenthal envisioned when he was growing up in New Jersey. It is one, he says, that offers a unique vantage point from which to look into questions of identity and ethnicity that go to the heart of who we are as a city, and as people.
Mr. Rosenthal said he had worked in health care marketing for years before having what he described as a big blowup with an employer in 2010. So he struck out on his own.
He bought an RV and refocused his business on drug testing for employers.
“I put this big cup of pee on the side of the truck,” he said.
It did not have the desired effect. The truck’s arrival often signaled to employees that a random drug test was imminent.
“People would see the pee truck coming and they were out of there,” he said.
As DNA testing became more widely available, he shifted his marketing. He had five employees at the time; they voted on the best slogan. He was the only one who favored “Who’s your daddy?”
But it was his truck.
Mr. Rosenthal hired a famous graffiti outfit, the Tats Cru, to paint the truck (he has since bought the second), and the reaction was immediate and overwhelming.
Last week, Mr. Rosenthal sat in one of the parked trucks in Midtown Manhattan, as a passing driver shouted a question.
The answer: $400.
Mr. Rosenthal’s company, Health Street, has over the last six years grown into one of the city’s leading providers of drug tests and, more recently, DNA tests. He has contracts with some 10,000 companies for tests and background checks, and estimates that between the trucks and his two clinics — one in Brooklyn and one in the Bronx — five DNA swabs per day are sent for testing.
The trucks even drew the attention of producers for VH1; he filmed an entire season of a reality television show called “Swab Stories.”
Mr. Rosenthal said he rarely went a day without being stopped and asked about his testing.
“It is a very private, closeted thing,” he said. “By putting this question out there in a big and splashy way, it sort of gets rid of some of the way that it is perceived. It gives permission for people, who may have had doubts or questions for years, to ask.”
“People will tell me the things they would never tell their closest friends and family,” he said. “These can be very intense and emotional moments.”
Some end in tears of joy, some in bitter disappointment and others simply in shock.
He told of an older Jewish woman who had been adopted as a child, and had been looking for her biological parents for years. Through diligent research she learned she had a sister, and through that sister found her mother, who would not, however, reveal the father’s identity.
It turned out that during World War II the mother had had an affair and became pregnant.
Through a series of complicated twists, the woman found someone she and her sister believed to be an uncle: a former Nazi soldier who had been taken prisoner during the war and later settled in the United States.
They tracked down the man, who by then was 92, and Mr. Rosenthal went to perform a swab on him. The next day the man died.
The test revealed the secret the mother had taken to her grave. The former Nazi soldier, the brother of the mother’s husband, was her baby’s father.
Mr. Rosenthal said he does not like to look at the results of a DNA test before he delivers the information, fearing that he might betray some emotion.
“You have to have empathy,” he said. “How you give someone difficult personal news can impact that person for the rest of their lives.”
“It is the essential question: ‘Who am I? Where do I come from?’”
He said that his years of performing DNA tests around the city have caused him to view questions of ethnicity and identity in a new way.
“No one really knows who they are,” he said.
People have been asking questions about paternity for as long as couples have been making babies, he said.
“Only now we have a test,” he said.